The work proposed in this Supplement request deals with sequencing of radioactively labeled polypeptides. The latter will be synthesized in vitro by translating their respective mRNA's in the presence of 20 labeled amino acids. The translation products will be separated by electrophoresis in polyacrylamide gels in sodium dodecyl sulfate and by immunological techniques. The separated peptides will be electrophoretically eluted from the gel, precipitated and subjected to Edman degradations using a Beckman sequencer. Detection of the radioactive PTH amino acids will be by qualitative (thin-layer chromatography) and quantitative (liquid chromatography) methods. The objective is to establish the validity of our recently formulated signal hypothesis. The essential feature of this hypothesis is the presence of a metabolically short-lived signal sequence, which comprises 10-20 amino terminal residues of all proteins (secretory, lysosomal, proxisomal) to be segregated in membrane-bound compartments. This signal sequence would trigger attachment of ribosomes to the membrane and is cleaved sometime thereafter but before chain completion. Our recent work has established the sequence of an amino terminal extension comprising 15 or 16 residues in numerous pancreatic secretory proteins. The striking sequence homology as well as the preponderance of hydrophobic residues in this sequence may constitute essential features for the proposed function of this signal sequence. Our investigations will be focused on the in vitro synthesized presecretory proteins and their proteolytic processing in the endocrine dog pancreas (insulin and glucagon), murine myeloma MOPC 41 DL 1 (IgG light chain) and bovine pituitary (ACTH, FSH, LH, LTH, TSH and growth hormone).